For this purpose, systems are known which comprise a closed circuit composed of a plurality of pipes arranged approximately at the roof or ceiling of the enclosed space; warm air is circulated within such pipes.
The heating effect is achieved by radiation from the surface of such pipes toward the floor by way of the presence of appropriately provided thermally insulating reflective screens.
A system of this type is disclosed in Italian patent No. 1,037,880 and GB-A-1448073, which comprises a burner arranged directly at the pipe and a fan for feeding the gaseous heating medium through the pipe, said fan being arranged upstream or downstream of the burner.
The burner is of the forced-draft type and is inserted at the pipe, which has the shape of a closed loop.
This solution has a drawback: the use of forced draft burners in fact generates in the pipe a preset pressure which forces continuous and accurate maintenance, which can be performed by extremely qualified individuals, to check for any leaks from said pipe.
Further heating systems are disclosed in prior art documents EP-A-0079526 and EP-A-0503489.
Further, the use of forced draft gas burners forces the provision of devices which are structurally complicated and difficult to fine-tune; the large number of moving mechanical parts makes the device prone to failures and therefore to considerable maintenance, and at the same time has high overall costs.
As a partial solution to this drawback, EP-647819 discloses a device for heating enclosed spaces which comprises at least one closed-circuit pipe which acts by thermal radiation, a burner for supplying a flame at the pipe for the direct heating of a heating medium, and a fan arranged upstream of said burner at said pipe in order to produce inside it a negative pressure, said heating medium being constituted by a mixture of gases and combustion air.
The burner is a Venturi-tube multi-hole burner, which provides a combined flame which lies within a fire tube which surrounds laterally said combined flame so as to provide a chamber in which the heating medium is dispensed laterally with respect to the fire tube and is circulated around it, after which the heating medium mixes downstream of said fire tube with a flame combustion gas and air drawn from outside due to the negative pressure produced by said fan and by jets of pressurized combustible gas within said Venturi-tube multi-hole burner.
Although this solution solves the drawbacks of the cited background art, the emission of pollutants is observed: heating devices of the radiating pipe type, which use forced-draft burners or with Venturi-tube burners or mixing tubes, in fact generate from combustion products whose values of CO (carbon monoxide), CO2 (carbon dioxide) and NOx (nitrogen oxides) are rather high.
Further, in the enclosed spaces in which these devices are installed, it is necessary to use, if they must be climate-controlled, also appropriately provided cooling devices, with the need to provide within the enclosed space separate pipes, ducts and electrical connections for supplying said devices and dispensing the air at a cooled temperature.
Moreover, known devices do not allow partial recovery of the energy that they generate.
As a partial solution to this drawback, so-called “cogeneration” systems are known which are usually constituted by a thermoelectric system for the combined production of electric power and heat energy, which is useful for increasing the efficiency of the fuel that is used.
However, these systems have considerable drawbacks: mainly they are very expensive, since they require a heating unit and therefore a boiler to generate and convey, through appropriately provided ducts, water in a circuit which comprises for example batteries for heat exchange.
Costs are therefore increased also by all the accessories for providing said pipes and circuits, to which it is necessary in any case to add all the circuits required if one wishes to provide climate control (cooling) of the enclosed space.
Known cogeneration systems include for example the ones known by the trade names Capstone, Elliott, and Turbec.
Currently it is also known to use microturbines to produce simultaneously electric power and hot water for the winter heating of buildings, or only to produce electric power, dispersing into the atmosphere the combustion gases.
It is also known to use microturbines to generate simultaneously electric power and hot water, which is sent subsequently into an absorber and produces refrigerated water for cooling and summer climate control of enclosed spaces in general.
However, even these solutions have drawbacks: for the winter heating of industrial enclosed spaces, one of the negative factors of the application of a microturbine is due to the fact that the hot combustion gases are used to heat the water normally to 80-90° C.; this water is then sent into heat exchangers, which in turn heat the air of the enclosed spaces.
This solution has a severe drawback, since the air, after being heated in the heat exchanger, decreases its specific gravity and tends to rise, generating inside the heated enclosed spaces high temperatures at the ceiling, which cause great heat loss and therefore great waste of energy.
For example, in a commercial or production space with a height of approximately 7 meters, ceiling temperatures of approximately 35° C. are found in order to have an air temperature of 18° C. at eye level.
Therefore, all the energy used to heat the air volumes that lie above the people to a temperature above 18° C. is a great energy waste.
Further, the hot gases heat the water by means of an exchanger, and such heated water can heat the air of the enclosed space by means of another exchanger: accordingly, long times to reach the steady state of the system are observed, since there are many transfer fluids involved in the heat exchanges.
Moreover, microturbine technology is currently very expensive, since said microturbines are derived from the aviation sector and it is extremely difficult to obtain variable-power microturbines which accordingly are small (for small buildings), medium-sized (for medium-sized buildings) and large (for large buildings).